Jim, your arithmetic is right, but I'm not sure about the assumptions. If I understand right, backspacing is the distance from the inside edge of the wheel lip to the mounting flange of a wheel, but offset is measured from the center of the wheel to the mounting flange, ignoring the distance from the outside edge of the wheel to the inside bead seat, which is about 1/4". If you need the exact flange-to-flange measurement, you really need the offset of the Daytons, or maybe get one and measure it.
I suspect that the 3.25" back spacing includes 0.25" from the inside edge of the rim to the inside of the wheel lip (where the tire bead mounts), then 3" from the inside of the lip to the center of the wheel, meaning that the offset on the Daytons could be zero. If so, the rear flange-to-flange dimension is 52.5", same as the rear track. See this link for wheel backspacing and dimensioning info:
How to measure Backspacing - GETAHELMET.COM
and this link for offset info:
Wheel Tech - Offset
Aww, never mind...Bob and Tom beat me to it and with better info!